24 REPTILES 



direction, and it was considered by many high authorities that 

 the resemblances existing between the pelvic and limb skeletons 

 of dinosaurs and birds were solely the result of adaptation, and 

 were not indicative of genetic relationship between the two 

 groups. It is true, that a guarded protest was raised by the 

 celebrated American palaeontologist Professor H. F. Osborn in 

 a paper published in the American Naturalist for 1900. In 

 this communication it was remarked that the passage from a 

 quadrupedal to a bipedal mode of progression would mark the 

 transition from the protorosaurian rhynchocephalians (the ad- 

 mitted ancestors of the ornithomorphous brigade of reptiles) to 

 dinosaurs, and consequently " that our present knowledge and 

 evidence justify us in saying that in this bipedal transition, with 

 its tendency to form the tibio-tarsus, the avian phylum may have 

 been given off from the dinosaurian ". 



Later opinion has, however, on the whole been markedly 

 against this partial reversion to the older theory of the descent 

 of birds from dinosaurs. Another well-known authority, Dr. 

 H. Gadow, points out, for instance, in the volume on reptiles 

 in the Cambridge Natural History that those dinosaurs which 

 exhibit the most marked avian resemblances did not come into 

 existence until about or after the time that birds had been fully 

 differentiated. After putting these later types out of court, 

 the author proceeds as follows : — 



" There remains only Anchisaurus of the Upper Trias, more 

 or less contemporary with Brontozoujn, which left its three-toed 

 foot-prints (Archceopteryx 1 has four well-developed toes) with 

 Zanclodon. Moreover, the most bird-like foot is either that of 

 the Theropoda [Megalosaurus, etc.] which, like Anchisaurus 

 and Zanclodon, differ from birds by the formation of the pelvis, 

 or of some of the latest Ornithopoda [fguanodou, etc.]. What, 

 then, is the good of selecting a number of bird-like features 

 from members of dinosaurs which we are bound to class in 

 different groups, and which existed, some in the lower, others 

 in the middle, or even in the latest Mesozoic periods ? " 



Dr. Gadow's contention appears to receive support from the 



British Museum specialist on reptiles, Mr. G. A. Boulenger, 



who, in a paper in the Proceedings of the Zoological Society for 



1904, to which reference has been already made, derives 



1 The toothed and long-tailed Upper Jurassic bird. 



